Synthesis, characterization, and photophysics of electroluminescent copolymers with a quinoline-based iridium complex in the main chain: A versatile method for constructing metal-containing copolymers

A series of novel soluble copolymers based on fluorene monomer in conjugation with carbazole and iridium complex monomers have been synthesized by the Suzuki polycondensation reaction. Iridium complexes based on 2-phenylquinoline or 1-phenylisoquinoline were incorporated into copolymers through a beta-diketonate ancillary ligand. The copolymers were characterized by using H-1 NMR, C-13 NMR, IR, and GPC. TGA/DSC measurements indicated that the copolymers have good thermal and morphological stability. An electrochemical investigation revealed that the HOMO and LUMO energy levels of the monomeric iridium complexes fall within those of the host polymer PFCz. The absorption spectra of the copolymers were dominated by absorptions from the fluorene-alt-carbazole backbone, while their photoluminescence (PL) spectra were dominated by emissions from the iridium complexes even at a feed ratio of the complex as low as 0.5 mol %. The copolymers PFCzIrphq emit orange-red light with an emission peak at ca. 590 nm, while PFCzIrpiq emits saturated red light with an emission maximum at ca. 620 nm, with a slight red shift compared with the emissions for the corresponding monomeric iridium complexes, respectively. Light-emitting diodes using the copolymers as emission layers under three types of device configurations were fabricated. The devices with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) doping display external quantum efficiencies significantly higher than those without PBD. A saturated red-emitting PLED with an emission peak at 628 nm, a maximum external quantum efficiency of 0.6% at the current density (J) of 39 mA/cm(2), and a maximum luminance of 541 cd/m(2) at 16 V was achieved from the device ITO/PEDOT/PFCzIrpiq3+PBD(40%)/Ba/Al.